1. Select 'Deploy Image' task
2. Select a syspreded image to be deployed (either from NS/PS or from http/https location).
3. Select the Product Key - windows only
4. Select the DA (if required) - windows only
5. Click 'Advanced...' button & goto Multicasting tab
6. Check 'To override the default multicast settings, change the values below.' if you want to override the default values for Threshold, Speed Limit & Timeout.
Note: Threshold :- Minimum number of client those should be present to run multicast (excluding master machine) mean if threshold is 2, multicast will happen only if task is scheduled on group of 3 or more machines Speed Limit: This determines the maximun speed at which master will multicast image. The best optimised value needs to be determined for individuals network setup. For VM client I have observed that speed value should be lesser than for physical machine. Speed=0 will multicast at maximum speed possible. Timeout: This value in minutes let all clients negotiate to determine master machine.

7. Save & schedule a run of the task on group of clients(threhold+1) in automation enviroment (PXE in your case).